Bismark rightly said at the end of the 19th century that the 20th century would be dominated by the USA and UK because they spoke the same language, One of Ukraine's weaknesses is that around 50% speak Russian and the rest Ukrainian. Put that with the west of Ukraine in some cases fighting with Hitler in WWII and the loss of 30 million Russians in WWII and it looks like Northern Ireland times 100. Russia wil annex Crimea plus the Eastern Ukraine.
It is not impossible as the Swiss have shown to have more than one official language in a country but it does make outbreaks of social unrest between linguistic groups more likely. Put this along with a recent history of war between lingustic groups as in Spain and social unrest will fester.
It gives the lie to the EU line that it has brought peace to Western Europe. The EU is a tower of Babel with the French hating the Germans, the Croats hating the Serbs etc. Hitler used the defence of German speaking minorities in other European contries to justfy his European invasions. The UK fought a war over Jenkin's ear. The Yanks are always mounting invasions to protect US citizens and interests. Putin is simply following a well trodden path.
What can the EU do about the Ukraine? Zilch just like the USA. It was the Red Army that defeated Hitler and they will see off Merkel and her EU chums if they interfere. I pray we stay out of it. We had to hand back Hong Kong island to China when they threatened to turn off the water supply. The EU is similarly powerless if the Russsians choose to turn off their gas supply. Thank God we do not have an EU army. It would be worse than useless.
Ukraine has brought home the political reality of the EU' s powerlessness. The US, Russia and China call the shots in their respective spheres of influence and in things like carbon dioxide production rule the whole globe. Please Rumpy, Frumpy and Barroso get real.